1. Field of the Invention
This invention relates to the production of hyperbranched .alpha.-olefin polymers.
2. Description of the Related Art
It is known in the art to prepare copolymers of at least one .alpha.-olefin and an .alpha.,.omega.-diene. For example, selected dienes have been copolymerized with .alpha.-olefins in order to introduce unsaturation into the polymer as a site for chemical reactions such as crosslinking. In U.S. Pat. No. 3,658,770 to Longi et al., it is taught that these dienes should be non-conjugated and should have two different kinds of double bonds, the first double bond being copolymerizable with the .alpha.-olefin and the second double bond being non-copolymerizable by Ziegler-type catalysts. Thus, useful classes of dienes for introduction of unsaturation into ethylene-propylene terpolymers are straight-chain and branched-chain acyclic dienes, single ring alicyclic dienes, and multi-ring alicyclic and bridged ring dienes, wherein one of the double bonds will copolymerize while the second is inert to the catalyst. Such useful dienes are 1,4-hexadiene, dicyclopentadiene and 5-ethylidene-2-norbornene.
The copolymerization of branched 1,4-dienes with ethylene, propylene or 4-methyl-1-pentene is similarly described in U.S. Pat. No. 4,366,296 to Kitigawa et al. While the copolymerization of propylene with .alpha.,.omega.-dienes of at least 6 carbon atoms using a Ziegler type catalyst in a hydrocarbon diluent is taught in U.S. Pat. No. 3,351,621 to Bacskai, the copolymerization has invariably led to a copolymer insoluble in hot decahydronaphthalene, indicative of the presence of cross-links and gel.
U.S. Pat. 4,931,526 discloses the preparation of relatively linear copolymers by copolymerizing a branched .alpha.-olefin having 5 to 10 carbon atoms and .alpha.,.omega.-non-conjugated diene having 6 to 20 carbon atoms using a solid inhomogeneous or heterogeneous catalyst containing a titanium, magnesium, halogen and electron donor component, an organo aluminum component and an electron donor. The copolymer is characterized as being partially crystalline and contains recurring units of the copolymerized diene component at least partially in cyclized form.
U.S. Pat. No. 3,984,610 discloses branched copolymers of ethylene and an .alpha.,.omega.-diene having at least 8 carbon atoms, wherein each double bond is readily polymerizable. The copolymers are partially crystalline and are prepared using a coordination catalyst comprising an alkyl aluminum chloride/vanadium oxychloride complex.
In addition, U.S. Pat. 5,504,171 discloses the preparation of crystalline, gel-free copolymers of an .alpha. olefin, e.g. propylene, and up to 5 mole % of an .alpha.,.omega.-diene. The copolymer is prepared using a solid-phase, insoluble, heterogeneous coordination catalyst, e.g., a Ziegler catalyst, in a solvent free medium. The product is characterized as containing unsaturated side chains and branched chains, and has a branching index (g') stated as ranging from 0.2 to 0.9. The patent discloses that soluble catalysts such as biscyclopentadienyl titanium (IV) dichloride-aluminum alkyl systems are unsuitable because gelled polymer products are obtained.
Hyperbranched polymers and dendrimers are a relatively new class of polymers which have a highly branched backbone structure. Dendrimers are exact, monodisperse structures built layerwise (in generations) around a core moiety, with a polymer branching point in every repeating unit. Typical dendritic macromolecules based on vinyl-cyanide and fumaryl dinitrile units are disclosed in U.S. Pat. 5,530,092. Hyperbranched polymers possess a number of characteristics which are similar to dendrimers but they are polydisperse and contain relatively linear segments off of which a plurality of highly branched segments are grown or attached. WO 97/06201 discloses the preparation of hyperbranched polymers containing a plurality of polyolefin arms linked to a polymer backbone by coupling a polyolefin pre-arm with a polymeric backbone or difunctional monomer containing functional groups reactive with the polymer pre-arm.
Hyperbranched polymers are characterized by the fact that once a backbone polymer segment is defined or chosen, the vast bulk of the molecular weight of the polymer is accounted for by the branched polymer segments and a smaller amount of the molecular weight is accounted for by the relatively linear segments to which the branched segments are attached. This means that even relatively high molecular weight hyperbranched polymers will exhibit a relatively low viscosity making them ideal candidates as rheology modifiers, oil additives, polymer plasticizers, low volatile organic content additives for theremosettable coatings and paints and similar applications. Unfortunately, however, hyperbranched polymers and dendrimers have been made by relatively expensive and laborious pathways which adds considerably to the cost.